The present invention relates generally to air brake systems for railroad trains and is particularly directed to detecting an overcharge or a separation in the brake pipe and automatically controlling the train locomotive until the condition is resolved.
One of the most critical aspects of the operation of railroad vehicles, particularly freight trains, is the predictable and successful operation of the air brake system. The air brake system is subjected to a variety of dynamic effects, not only as a result of the controlled application and release of the brakes through changes in the brake pipe pressure, but also due to varying conditions encountered by the train.
FIG. 1 illustrates a typical prior art brake system employed by a railway freight train. The train brake system comprises a locomotive brake system located on a locomotive 100 and a set of car brake systems located on a set of railway cars illustrated by car 200. The application and release of braking action is generally controlled by an engineman within a locomotive 100. The locomotive 100 contains an air brake control system 102, including a controllably pressurized brake pipe 101. The pressurized brake pipe 101 is connected (via one of a series of cut-out valves 120) to the train air line 201. It is through the train air line 201 that air brake pressure is supplied to each of the cars 200 of the train. The brake control system 102 also includes an air supply input link 111 for supplying, under pressure, fluid (air) through which the brake pipe 101 and the train air line 201 are charged. Ultimately, the air brake control system 102 controls the operation of the pneumatically operated brake shoes 233 at each of the wheels 235 of the car 200.
A flow measuring adapter 113, and its associated charging rate gauge 115, are connected to the air supply link 111. The flow measuring adapter 113 and the charging rate gauge 115 measure and display the charging rate (as a differential pressure) of the brake control system 102. The output terminal 116 of the flow measuring adapter 113 is connected to input port 121 of a relay valve 117. A bi-directional port 122 of the relay valve 121 is coupled to the brake pipe 101. The relay valve 117 further includes a port 123 that is coupled through an air pressure control link 103 to an equalizing reservoir 105. The pressure control link 103 is also connected to a pressure control valve 107 through which the equalizing reservoir 105 is charged and discharged in the process of a brake operation. A port 124 of the relay valve 117 is controllably vented to the atmosphere as an exhaust port. Coupled with brake pipe 101 and air pressure control link 103 are respective pressure measuring and display devices 131 and 133. The brake pipe gauge 131 measures the air pressure in the brake pipe 101 and the equalizing reservoir gauge 133 measures the pressure in the equalizing reservoir.
The components of the car air brake control system 102, include a control valve 203, having a port 221 that is coupled to the train airline 201. Control valve 203 also includes a port 222 that is coupled to a pressure storage and reference reservoir 205. Finally, the control valve 203 includes a port 223 coupled to the air brake cylinder 231 that controls the movement of the brake shoe 233 against the wheels 235 of the car 200.
In operation, the cut out valve 120, through which brake pipe 101 and successive segments of the train air line 201 are coupled in serial fluid communication, is assumed to be fully open, so that there will be a continuous brake pipe/air line fluid path between the locomotive 100 and all of the cars 200 of the train. The brake system is initially pressurized by the operation of pressure control unit 107, which controls the air supply to line 103 so as to fully charge the equalizing reservoir 105. The relay valve 117 is then operated to couple port 121 with port 122 so that air is supplied there through to the brake pipe 101 and thereby to the train air line 201, to charge the brake pipe/air fluid line path 101/201 to the predetermined charging pressure. This pressure (typically 72 psi. on UIC trains) is established by the pressure of the equalizing reservoir 105 within the locomotive 100. The pressure within the brake pipe 101 and the train air line 201 is determined to have reached the correct pressure, as established by the pressure in the equalizing reservoir 105, when the pressure at port 122 (connected to the brake pipe 101) matches the pressure at port 123 (connected to the equalizing reservoir 105).
Through control valves 203 in each of the cars 200, the pressure storage and reference reservoirs 205 are filly charged, to thereby establish a reference pressure for maximum withdrawal of the piston of each air brake cylinder 231 and thereby complete release of the brakes 233 for each of the cars 200.
When the engineman desires to apply brakes to the wheels of the train cars 200, he operates pressure control unit 107, typically via a handle-operated control valve, which is coupled to the air pressure control link 103. Operation of the pressure control valve 107 causes a partial venting of air pressure control link 103 and thereby a reduction in the pressure within the equalizing reservoir 105. This reduction in pressure in the equalizing reservoir 105 is sensed by the relay valve 117 at port 123. In turn, this causes the bi-directional port 122 to be coupled to the exhaust port 124 and thereby exhaust the brake pipe 101 to the atmosphere, until the pressure within the brake pipe 101 equals the pressure of equalizing reservoir 105.
As the pressure in the brake pipe 101 and therefore within the train air line 201 drops, the control valves 203 in each of the cars 200 sense the pressure reduction in the train air line 201 by comparison to the pressure in the pressure storage and reference reservoir 205. This causes a corresponding increase in the pressure applied to the brake cylinders 231 from port 223, resulting in an application of the brake shoes 233 against the wheels 235 in proportion to the sensed pressure reduction in the train air line 201. Further pressure reductions in the equalizing reservoir 105 by the engineman produce corresponding pressure reductions in the train air line 201 and, thereby, additional braking effort by the brake shoes 233 in each of the cars 200. In summary, the intended operation of the brake system in the cars 200 and specifically the braking effort applied in each of the cars 200, is proportional to the reduction in pressure in the equalizing reservoir 105 within the locomotive 100.
When the engineman desires to release the train car brakes, he operates pressure control unit 107 to effectuate a recharging of the air brake control system 102. This is accomplished by bringing the pressure within the equalizing reservoir 105 back to its fully charged state as described above. With equalizing reservoir 105 recharged, there is again a pressure differential (but opposite in sign to the previous pressure drop in the pressure line 103) between the ports 122 and 123 of the relay valve 117. This increase in pressure is sensed by the control valves 203 in each of the cars 200 so as to cause the brake shoes 233 to be released by the action of the brake cylinder 231.
During normal operation, the application and release of the brakes is controlled in accordance with the above described sequence of events. However, there may be circumstances dictated either by action taken by the engineman or by other unpredictable events, which create the potential for unsafe operation of the braking system. One of these conditions relates to the standards and operation of the brake system on European trains having a UIC (Union Internationale de Chemins Fer) brake system.
UIC trains may have different operational pressures within the brake pipe 101. That is, there is not a standard brake pipe pressure for the operation of all UIC trains. As train cars are decoupled from one train and then combined to form a new train consist, the pressure storage and reference reservoirs 205 in each of the cars may be precharged to different levels, due to the different brake pipe pressures on the source trains. Uneven precharging among the cars 200 can cause uneven braking, sticking brakes, or possibly no braking on some of the cars when the engineman of the new train calls for brake application by reducing the brake pipe pressure. The engineman has no visual information as to the braking status, i.e., on or off at each car. He assumes that if the pressure in the brake pipe 101 is at a normal level (e.g., 72 psi) then the brakes of the cars are released, and if the brake pipe pressure is lower than normal, then the brakes are applied to some extent.
To overcome this problem, the UIC trains are required to undergo an assimilation process to neutralize this uneven pre-charge condition among the cars 200. The successful execution of the assimilation feature allows all cars 200 to be charged to the current brake pipe setting. This is accomplished by overcharging the brake pipe 101 (and thus the train line 201) to a level much higher than the normal operating brake pipe pressure and then slowly reducing the brake pipe pressure through the relay valve 117 and the exhaust port 124. Typically, the slow pressure reduction process takes one to two minutes. This pressure reduction occurs at a very slow rate (so that the brakes are not applied during bleed-down) and when it is completed, all cars 200 will have their pressure storage and reference reservoirs 205 equalized to the new pressure of the brake pipe 101 and the train air line 201.
If the assimilation feature is initiated so that the brake pipe 101 is overcharged and then there is an interruption in the assimilation process (e.g., a train emergency or the failure of the assimilation system) the brake equipment (specifically the pressure storage and reference reservoirs 205) in each of the cars 200 may be left in an overcharged state. For example, assume the assimilation feature is intended to raise the pressure in the brake pipe 101 and the air train line 201 to 83 psi to overcome the overcharged state in one or more of the cars 200. The assimilation feature is initiated and the pressure in the brake pipe/air train line 101/201 increases to 83 psi. The pressure is then reduced at a very slow controlled rate by an assimilation control valve. If the assimilation process is now interrupted by an emergency condition, for example, at a time when the pressure had been reduced to 80 psi, then the pressure storage and reference reservoirs 205 in each of the cars 200 will have a pressure of 80 psi, rather than the expected pressure of 72 psi.
After the emergency is over and the train is ready to return to normal operation, the engineman releases the brakes and the brake pipe pressure is set at its normal release setting of 72 psi. Since the cars 200 are charged to 80 psi, they sense a reduced pressure of 8 psi. Specifically, this reduction in pressure is sensed by the control valve 202, by comparison with the pressure in the pressure storage and reference reservoir 205. As a result, there is a brake application corresponding to an 8 psi brake pipe pressure reduction. The engineman will have no indication that the car brakes are applied, which can result in undesirable and possibly dangerous operating conditions. For example, additional motive effort will be required to move the train when the brakes are applied, and more fuel will be consumed. The brake application will cause the build up of heat in the brake shoes 233 and the wheels 235, possibly resulting in wheel tread damage, wheel cracks and train derailment. Also, since the train cars are dragging, the coupler forces will increase and could, in fact, exceed the coupler maximum force threshold and thereby cause separation of the train.
The situation is exacerbated when LOCOTROL(copyright) (a registered trademark of GE-Harris Railway Electronics, L.L.C.) control units are included in power trains that are operated with head-end and remote locomotives. In this case, a remotely-controlled locomotive could generate high pushing forces on cars ahead of it in the train, especially if these cars had the brakes set. As a result, the cars might be pushed off the track and derailed.
Another possible scenario proceeds as follows. Assume the assimilation pressure reduction process was interrupted when the brake pipe 101 and air train line 201 were charged to 79 psi, with a normal operating pressure is 72 psi. If the engineman wishes to apply the brakes, he does so through the pressure control valve 107 by exhausting the brake pipe line 101 to the atmosphere, via relay valve 117 and the pressure control link 103. The brake pipe pressure suddenly goes to 0 psi and the pressure in the train line 201 follows in due course. The control valve 203 senses the pressure differential between the train air line 201 and the pressure storage and reference reservoir 205, and applies the brakes. Continuing with this scenario, assume that the engineman now desires to release the brakes by increasing the pressure in the brake pipe line 101 to its normal value of 72 psi. But recall, that the reference storage and reference reservoir 205 has a pressure of 79 psi. This pressure differential of 7 psi will be sensed by the control valve 203, interpreted as a request for braking action, and the brakes will remain partially applied, even though the engineman has initiated a complete brake release.
Train separation is another emergency condition that must be detected and countered on UIC trains in a manner different than trains operating with North American type braking equipment. When a train separation occurs on a North American-type train, the pressure of the brake pipe 101 immediately goes to zero at the separation point and each car 200 detects this rapid drop in brake pipe pressure. Each car 200 then activates its emergency valve and in this way, the train separation emergency is quickly propagated through the adjacent cars. The emergency valve also causes application of the brakes 233 on each car 200. Emergency status is also propagated to the locomotive and when detected there, the charging of the brake pipe 101 through the relay valve 121 is suspended. Also, the locomotive throttle is commonly set to an idle position.
UIC train cars are not typically equipped with emergency valves and, therefore, cannot detect and propagate a train separation emergency. When a train separation occurs, the brake pipe 101 at the point of separation goes to zero pressure and the entire brake pipe must then exhaust through the separation break point. Depending upon the location of the separation, the time to completely exhaust the brake pipe 101 can be considerable, at least in relative terms. Since there is no propagation of the train separation emergency to the locomotive, the locomotive maintains its throttle position and continues to supply air to the brake pipe 101 until such time as the brake pipe 101 pressure drops below a predetermined cut off value. The time required for the locomotive brake pipe 101 to reach the cut off value could be considerable, and in some cases, it may never reach the cut off point.
The detection of train separations becomes much more significant when LOCOTROL(copyright) distributed power trains are operated, since an undetected train separation in front of the remotely controlled locomotives can result in these locomotives remaining in the powered state and, thus, create potentially dangerous in train forces near the separated cars.
In accordance with one aspect of the present invention, the above described shortcomings of the conventional UIC brake control systems using the assimilation feature are obviated by a new and improved brake control system. In one embodiment, the brake control system of the present invention monitors the brake pipe pressure at the locomotive to determine when it is in an overcharged state. If the slow reduction of the brake pipe pressure following the overcharged state is interrupted before reaching the normal brake pipe pressure, this occurrence is detected by the present invention. When the event that caused interruption of the assimilation process has ended, the brake control system reinitiates the assimilation process and recharges the brake pipe to the higher-value. Once recharged to the higher value, the slow pressure reduction process is initiated and when completed, the system has returned to its nominal pressure.
In another embodiment of the present invention, when interruption of the slow pressure reduction process is detected, the locomotive traction is automatically placed in to an idle state and the engineman alerted to the overcharged condition of the car pressure storage and reference reservoirs 205.
In yet another embodiment of the present invention, on UIC trains, a brake pipe separation is detected and the locomotive is automatically placed into an idle state. Detection is accomplished by monitoring the brake pipe pressure and airflow.